Not enough caster sugar. What's the best alternative?

[DevonFolk]

I'm making a basic chocolate sponge but just realised I'm about 90g short of caster sugar. I have various other sugars in the cupboard but not sure which would be best. Any suggestions? Going out for more isn't an option!

If you whizz granulated sugar in a food processor for a few seconds it turns into caster sugar. But don't do it for too long, or you get icing sugar instead.

Granulated will be absolutely fine.

You might be able to get away with just not using the full amount?

The structure of a typical sponge doesn't depend on sugar, it's just there as a sweetener.

I've experimented over the years and found that using up to 25% less of the quantity in the recipe has no effect on the final result.

Thank you!